Question

1. in the ground state, an atom of each of the elements in group 2 has a different

(1) oxidation state
(2) first ionization energy
(3) number of valence electrons
(4) number of electrons in the first shell

Explanation:

Group 2 elements (alkaline earth metals) have 2 valence electrons. Their first ionization energy, oxidation state, and number of electrons in the first shell (which is 2 for all elements except hydrogen) are not different. However, as we move down Group 2, the first ionization energy decreases due to increased atomic size and shielding. But the key commonality is that all Group 2 elements have 2 valence electrons.

Answer:

(3) number of valence electrons